Field of the Invention
The present invention relates to a process for producing a liquefied coal oil by a two step hydrogenation reaction of coal, and a catalyst useful for the second hydrogenation reaction. More particularly, the present invention relates to the hydrogenation treatment of a liquefied product of coal by a catalyst composed of a carrier such as alumina or silica alumina, and a metal of Group VI-A and a metal of Group VIII of the Periodic Table supported thereon, wherein an alkali metal compound and/or an alkaline earth metal compound is incorporated to the catalyst.
It is well known that a catalyst wherein a metal of Group VI-A of the Periodic Table such as molybdenum and a metal of Group VIII such as cobalt or nickel are supported on a carrier such as alumina, is catalytically effective for the hydrogenation treatment of a reaction product obtained by the first hydrogenation reaction of a coal such as bituminous coal, sub-bituminous coal, brown coal or lignite by e.g. hydrogenolysis or solvert extraction.
However, such hydrogenation reaction products, particularly the high boiling point fractions having boiling points of at least 400.degree. C., contain substantial amounts of highly condensed aromatic hydrocarbons or aromatic compounds containing hetero-atoms such as nitrogen or sulfur in their molecules, which cause deactivation of the catalyst. In the hydrogenation treatment of such first hydrogenation reaction products, there used to be difficulties such as deactivation of the catalyst due to the formation of coke on the catalyst or clogging of a catalytic bed due to coking which takes place in the catalytic bed in the case of a continuous hydrogenation treatment in a fixed-bed type reactor.
The present inventors have conducted extensive researches to develop a process and a catalyst which are highly effective for the hydrogenation treatment of the first hydrogenation reaction product in a two step hydrogenation reaction of coal and which do not bring about the formation of coke on the catalyst. As a result, it has been found that when an alkali metal compound or an alkaline earth metal compound is used in combination with the catalyst carrying a metal of Group VI-A and a metal of Group VIII of the Periodic Table, the catalyst exhibits a superior catalyst activity, whereby the coking is substantially suppressed and the deterioration of the catalytic activity in the continuous hydrogenation treatment reaction is prevented to a substantial extent. The present invention has been accomplished based on these discoveries.